1. Field of the Invention
The present invention relates generally to dissection cannula used for forming an elongated cavity in tissue planes. The present invention relates specifically to an everting balloon dissection cannula.
2. Description of Background Art
Present methods for the formation of an elongated cavity involve the use of blunt probes that are pushed through body tissue to accomplish the dissection. The force exerted by the passage of mechanical probes may lead to blood vessel avulsion and trauma to tissue and internal organs. A method of atraumatic blunt dissection is desired, preferably a method of accomplishing this blunt dissection under visual control.
Several balloon catheters are disclosed in various issued patents and publications. Exemplary everting balloon catheters used for arterial dilation include U.S. Pat. No. 4,271,839 (Fogarty et al., Jun. 6, 1981), U.S. Pat. No. 4,479,497 (Fogarty et al., Oct. 10, 1984), U.S. Pat. No. 4,863,440 (Chin, Sep. 5, 1989), and U.S. Pat. No. 4,526,175 (Chin et al., Jul. 7, 1985).
Single lumen everting balloon catheters, such as that disclosed in the Fogarty et al. '839 patent, do not provide a channel for an endoscope. Even if an endoscope were inserted into the disclosed single balloon lumen, the endoscope would be unable to track down to the distal part of the catheter due to the presence of the balloon positioned at the end of the catheter. In such a construction, structures lying outside of the balloon would be outside the range of view for that endoscope. The folds of balloon lying within the catheter, as disclosed in the Fogarty et al. '839 patent, do not provide an optically clear viewing window, as multiple layers of transparent balloon material distort possible imaging. A single layer of balloon material is needed for successful visualization.
Double lumen everting balloon catheters, such as those disclosed in the Fogarty et al. '497 and the Chin '440 patents, have a through-lumen 102 that permits the passage of an endoscope 100. However, an endoscope 100 used in conjunction with those disclosed catheters is unable to monitor the dissection process, since the endoscope 100 lies within the central lumen 106 proximal to the everting balloon 104, as illustrated in FIG. 1A. As the balloon 104 everts from the catheter, the internal inflation pressure squeezes the walls of the balloon and closes off the distal viewing channel 108, as illustrated in FIG. 1B. Also, the area that requires monitoring during balloon dissection is located at the advancing front of the everting balloon 104. This area corresponds to the balloon/tissue interface subject to forces that cause tissue separation. Thus, an endoscope 100 in the central lumen 106 of existing double lumen everting balloon catheters is unable to view the tissue separation area, since a double layer of balloon membrane lies between the endoscope 100 and the tissue blocking the endoscopic line of sight 110, as illustrated in FIG. 1C. This double layer obscures and distorts the viewing image.
The catheter disclosed in the Chin et al. '175 patent has a looped lumen which does not accommodate a rigid endoscope. A balloon cannula has been tested which performs blunt dissection using a long, tubular, generally inelastic balloon that is rolled up outside the lumen. As illustrated in FIGS. 2A and 2B, the rolled up balloon 104 is introduced to the tissue cavity 112. As the balloon 104 is inflated and unrolled, as shown in FIG. 2B, it remains partially folded as it inflates, forming a generally spherical cavity 112. This spherical cavity 112 is contrasted with the desired elongated cavity 114.
Other versions of balloon dissection cannulae are commercially available, for example, from Origin Medsystems, Inc., the assignee herein. One such version uses a spherical, elastomeric balloon, and another such version uses a generally elliptical, inelastic balloon that is rolled up outside the lumen. These cannulae dissect generally spherical cavities.